This invention relates to the nuclear-reactor art and has particular relationship to reactors, typically breeder nuclear reactors in which tritium is produced. As is well known in the art, a breeder nuclear reactor produces more fuel than it consumes during the generation of useful energy. The consumable fuel contains fissile materials which undergo fission and produce heat. The heat is transferred to a reactor coolant which flows through a reactor vessel wherein the fissile fuel is contained. The heat thus acquired by the reactor coolant is used to generate steam which is then used to produce electricity. Typically in this type of reactor a void exists above the level of reactor coolant within the reactor vessel. The void is generally filled with an inert gas so as to not adversely effect the reactor coolant. This gas is commonly referred to, in the nuclear art, as the reactor cover gas (see Reactor Handbook, Volume IV, Second Edition (1964) published by Interscience Publishers, p.p. 327 and 790).
In this type of nuclear reactor, tritium results typically from reactions of neutrons and alpha particles; that is, helium nuclei, in the boron 10 of the control rods and in the lithium 6 impurities in the fuel and by ternary fission. The collision of a neutron with an alpha particle results in the ejection of a proton from the alpha particle producing tritium nucleus which is converted into tritium by absorption of an electron. Tritium is radioactive emitting beta particles and becoming converted into Helium 3.
Tritium is produced both in the coolant fluid, typically sodium, and in the reactor-cover-gas, typically helium. In either case the tritium contaminates the coolant fluid in the primary loop and, because it diffuses through metals it may contaminate the secondary fluid and structures in the vicinity of the nuclear reactor. It is then desirable in the interest of health and safety to minimize the concentration of tritium in the coolant fluid and reactor-cover-gas; indeed, it is desirable to reduce the concentration of tritium to zero.
In accordance with the teachings of the prior art, the tritium is reduced by operating continuously cold traps in the reactor fluid channels which crystallize out hydrogen and its isotopes. Another tritium suppression process is disclosed in application Ser. No. 261,476 filed June 6, 1972 to Richard Paul Colburn, entitled Method For Removing Fission Products From a Nuclear Reactor Coolant, and assigned to Westinghouse Electric Corporation. In accordance with Colburns's teachings, the coolant fluid is continuously cycled through a bypass where hydrogen is added to it and the hydrogen, deuterium, and tritium are precipitated as sodium hydrides. This process is referred to as cold slagging.
Continuous cold trapping or cold slagging which the above-described prior art processes require presents serious difficulties. The cold trap, while in operation, traps out, not only the hydrogen isotopes, and oxygen, but also other radioactive elements which otherwise may readily remain in the fluid without hazard. The cold trap as a result of the continuous cold trapping, then soon becomes radioactively hot so that it cannot be conveniently handled. Like reasoning is applicable to cold slagging which operates at a substantially higher rate than cold trapping.
To avoid continuous trapping, it is desirable to monitor the tritium in the fluid and when the tritium reaches a preset threshold to remove it by effective cold trapping or slagging for a relatively short time interval. Such a preferred procedure demands proper and reliable monitoring of the fluids.
In accordance with the teachings of the prior art, attempts have been made to carry out the monitoring by analysis of coolant samples. Typically, samples of sodium are removed from the test-loop system or the reactor vessel, the hydrogen and its isotopes separated out and the quantity of tritium determined by radiometric measurement. This process is tedious and time consuming; there may be excessive build up of tritium during the time which elapses between successive analyses. In addition, this process is unreliable because segregation occurs during the bypass sampling. Also, this monitoring process is not continuous. Sudden large changes in the tritium concentration, which reveals a defect in the operation of the reactor, are not quickly detectable.
It is an object of this invention to overcome the above desired disadvantages and deficiencies of the prior art and to provide for the prompt, effective and reliably continuous monitoring of the tritium content or concentration of reactor fluid, without necessitating removal and analysis of fluid samples and in such manner that the content or concentration at any time shall be determinable in a short time interval.